Traction motor gear lubricant



TRACTION MOTGR GEAR LUBRICANT William J. Scheifley, Richard C. Givens, and Melvin R.

Hefty, Port Arthur, Tex., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application December 23, 1955 Serial No. 554,939

Claims. (Cl. 252-42.1)

This invention relates to a new traction motor gear lubricant characterized by improved low temperature performance and freedom from thickening in service.

The traction motor gears of diesel electric motors have been lubricated very successfully for many years by a product comprising 35 to 65 percent residual oil and 65 to 35 percent of an asphalt derived by air blowing of an asphaltic residuum. These asphalt-thickened residual oils have given excellent protection against gear wear but have had two major deficiencies, namely thickening caused by poor oxidation resistance and a tendency to set up at low temperatures. These deficiencies have limited the use of asphalt-thickened residual lubricants in the so-called tight gear cases of the EMD diesels and in winter lubrication of traction motor gears in general in northern areas.

This invention is concerned with the development of a superior traction motor gear lubricant which retains the excellent protection against gear wear of the previous asphalt-thickened lubricant and at the same time exhibits good low temperature performance and freedom from oxidation thickening in service.

The traction motor gear lubricant of this invention comprises more than 94 percent by Weight of a sulfurized high viscosity residuum and 1 to 3 percent by weight of an alkali metal soap derived from a fat. The sulfurized residuum has a sulfur content between 0.7 and 1.3 weight percent. The lubricant of this invention also usually contains 1 to 3 percent by weight of a residual oil which is used as a carrier in which to saponify the fat to soap prior to the mixing of soap and the sulfurized residuum.

The alkali metal soap component of the gear lubricant of the invention can be derived from animal fats and vegetable oils, from the fatty acid components of these glycerides or from their monoesters. Tallow, lard, castor oil, hydrogenated castor oil, fish oils, soybean oil, stearic acid, oleic acid, l2-hydroxystearic acid, and palmitic acid are examples of materials that can be used to form the alkali metal soap. Sodium and lithium soaps can be used but sodium soaps are generally employed because of their lower cost. It is readily apparentthat the composition of the alkali metal soap component is not critical and that the main criteria in determining its selection is cost. Sodium tallowate, the product of reaction of tallow and sodium hydroxide, is extensively employed as the soap component since it is one of the cheapest alkali metal soaps.

The concentration of the alkali metal soap component falls between 1 and 3 weight percent of the gear lubricant and usually between 1.5 and 2.5 weight percent. An alkali metal soap content of about 2.0 weight percent has been found to give optimum thickening properties and low temperature properties to the gear lubricant.

The residual oil employed as a carrier for the introduction of the alkali metal soap into the sulfurized residuum also constitutes 1 to 3 weight percent of the lubricant composition. Since it is convenient to use the residuum carrier in an amount equal to that of the alkali metal Patent ice soap, a 50-50 blend of alkali metal soap and residual oil in an amount equivalent to about 4 weight percent of the total gear lubricant has generally been employed.

The composition of the residual oil carrier is also not critical. Unrefined parafiin base, naphthene base and mixed base residua are used. An unrefined mixed paraffin-naphthene base residuum having an SUS at 210 F. of 750 has been extensively used as a carrier oil in the gear lubricants described hereafter.

The sulfur-containing residuum, which usually constitutes to 97 percent of the gear lubricant, is prepared from a residuum having an SUS viscosity at 210 F. of at least 950 and preferably between 1000 and 1500. Unless the residuum from which the sulfur-containing resiluum is formed has an SUS at 210 F. of 950 or over, the resulting sulfurized product does not have a sufficiently high film strength as measured by the modified fourgram Timken test. High viscosity residua are obtained by subjecting lube oil fractions to more severe vacuum distillation. A particularly preferred charge for sulfurization is a mixed paratfin-naphthene base residuum having an SUS at 210 F. of about 1010.

Reaction of the high viscosity residuum with sulfur is effected at temperatures between about 400 and 470 F. and requires a reaction period of at least 6 hours. The residuum is reacted with 1.5 to 4 weight percent powdered sulfur with 2 weight percent sulfur normally bemg used for sulfurization. The reaction is continued until a sample, which has been air-blown to free it of H 8 gives a negative copper strip corrosion test. Details of a continuous process for preparing sulfur-containing residuum are presented hereafter.

The sulfur-containing residua. obtained under the foregoing general reaction conditions from residua having an SUS viscosity at 210 F. of at least 1000 have the following general properties:

Sulfur content, weight percent 0.8 to 1.3 SUS viscosity at 210 F. 1000 to 1500 Pour, F. 40 to 65 70 to 100 Flash, F above 530 The three most important properties of a traction motor gear lubricant are low temperature performance, resistance to thickening by oxidation, and, of primary importance, an ability to prevent gear wear. The ability of the gear lubricant to prevent gear wear is measured by the modified four-gram Timken test which measures film-strength. Low temperature performance properties are measured by the simulated TMG torque test while resistance to oxidation thickening is measured by the modified U. S. Steel Corporation gear oil thickening test, the oxidation thickening test and the ASTM bomb oxidation test. A brief description of these tests is presented hereafter.

The modified four-gram Timken test is run on the Timken machine by a procedure involving lubricating the ring by spreading four grams of lubricant evenly on its surface, applying a 30 lb. load and running the machine until the ring scores. The time required for scoring is noted and reported.

The simulated TMG torque test, which evaluates the low temperature starting characteristics of the lubricant, is run in an adapted washing machine transmission; the test unit and lubricant are cooled to test temperature and the power requirement for starting the unit determined by means of a recording watt meter. The test is considered a failure when the starting power exceeds 4,000 watts, when the electric motor smokes on starting or when the motor is on starting windings for 7 seconds or longer.

The oxidation thickening test, also called a static oven heating test, involves measurement of penetration before and after heating in an oven for prescribed periods of time. In this test the penetration is initially determined, the lubricant placed in a 210 F. electrically heated natural convection oven for a thousand or a fifteen hundred hour period. At the end of the period, the penetration is again measured and the degree of change is calculated on the basis of the initial test.

The modified U. S. Steel Corporation gear oil thickening test involves passing liters of dry air through 300 ml. of test oil, which is maintained at a temperature of 203 F. during the 312 hour period in which the air is passed through the test oil. At the end of this period the percent decrease in penetration is measured. A small percentage change in worked penetration indicates a lubricant which is stable to oxidation thickening.

The ASTM bomb oxidation test is well known in the art and involves measuring the pressure drop in p. s. i. g. obtained after a 100 hour period during which the test lubricant is subjected to oxidation in a bomb at prescribed temperature conditions.

The mixed base residuum is sulfurized in a continuous process at a temperature between 420 and 475 F. An initial quantity of residuum and sulfur is charged to the reaction system comprising a heater, a reaction zone and a vacuum stripping zone. The initial reaction mixture is recycled through the heater, reaction zone and vacuum stripping zone in that sequence at a temperature of about 440 F. until a sample drawn from the vacuum stripping zone gives a negative copper strip corrosion test at 212 F. after 1 hour of contact. Thereafter, additional sulfur and residuum are charged in proportions such that the residuum constitutes 98 percent of the charge and the sulfur 2 percent. An equivalent amount of reaction product is withdrawn (at the same rate that the charge is introduced) from the vacuum stripping zone wherein steam stripping removes H 8 from the reaction product. The resulting product has the properties heretofore set forth for the sulfur-containing residuum.

The preparation of a large batch of sulfurized residuum having a sulfur content of about 0.9 weight percent and an SUS viscosity at 210 F. about 1160 is shown in Example 1.

EXAMPLE 1 120 barrels of mixed high viscosity paratlin-naphthene base residuum having an SUS viscosity at 210 F. of 1100 were charged to the sulfurization reaction system. The residuum was recycled through a heater and reactor continuously at the rate of about 40 barrels per hour until the reactor outlet temperature was about 325 F. The vacuum stripping zone was then added to the system so that the hot residuum cycled through heater, reaction zone and stripping zone in the stated sequence. Steam was charged to the stripping zone at the rate of 580 lbs. per hour. When the temperature of the residuum reached about 440 F. powdered sulfur was added until it constituted' about 2 weight percent of the total charge. Circulation of the sulfur residuum mixture was continued through the heater, reactor and stripping zone until a sample, which had been airblown at 180 F. for about /2 hour to remove H 8, gave a peacock or better copper strip corrosion test at 212 F. for one hour. After a sample showed negative in this test, additional residuum was charged at the rate of about 16 to 18 barrels per hour plus sulfur in an amount suflicient to constitute two percent of the total charge. While the reaction mixture was recycled at about 30 obls. per hour, the reaction product was withdrawn .at a rate equivalent to the rate of charge from the vacuum tower. The reaction product was tested for copper strip corrosion at regular intervals. (If a sample was elf-test, addition of charge and withdrawal of product were stopped and the reaction mixture was circulated through the system until a withdrawn sample was on-test.) A total of 111,656 pounds of mixed base residuum and 2280 pounds of sulfur were o lowate and 1.5 percent sodium tallowate 4 charged to the reaction zone and 111,237 pounds of sulfurized residuum were obtained. The product contained 0.92 percent sulfur, had an SUS viscosity at 210 F. of 1163, a VI of 82, a pour of 45 F., and gave a negative copper strip corrosion test at 212 F. for 1 hour.

A traction motor gear lubricant was prepared by adding to the sulfur-containing residuum obtained in the foregoing plant manufacture, a 50-50 mixture of sodium tallowate and a raw mixed paraffin-naphthene base residuum. The details of the preparation of this product are shown in Example 2.

EXAMPLE 2 A mixture of sodium tallowate and unrefined mixed paratfin-naphthene base residuum having an SUS viscosity at 210 F. of 750 was prepared by saponification of 10 pounds of hog tallow with 3 pounds of 49% caustic in the presence of 5 pounds of water and 10 pounds of residuum at a temperature of to F. The saponified mixture was then dehydrated at a temperature between 260 and 300 F. To the resulting mixture, comprising 10.6 pounds of sodium tallowate and 10 pounds of mixed base residuum, 332 pounds of sulfur-containing residuum manufactured as in Example 1 were added with stirring as the reaction mix slowly cooled to about 130 F.

After addition of all the sulfur-containing residuum, which took about 30 hours, the product was pumped through a 60 mesh screen into drums. The resulting product, which had an approximate composition of 94 percent sulfur-containing residuum, 3.0 percent sodium tallowate and 3.0 percent residuum, was a semi-fluid stringy grease.

From this lubricant containing 3 percent soap, two additional lubricants containing 2 percent sodium talby the addition of 15 and 20 pounds, respectively, of sulfur-containing residuum. The properties of these three lubricants are shown in Table I.

Table 1 Percent Soap Concentration Test Results ASTM Penetration, 77 F.:

Unworked 297 324 346. 363 377 386. O 37, 3G 33, 34 33, 32. Drop/100 Hr. Mod. 4-Gran1 Timken Test: 30# Load- 18, 2O 15, 17 20, 15.

Minutes to Fail. Simulated TMG Torque Test:

Temp., "F 50 5O 50. Starting Load. Max. Watts 3, 500 3, 700 3,600. Time on Starting Winding, Sec 1. 7 6 6. Oven Oxidation Test, 210 F.:

ASTM Penetration, 77 F.Percent Decrease After 1,500 Hr.:

Unworked 30. 0 24. 6 18.2. W0rkcd. 1. 4 3.2 T00 soft. Appearance OK OK K. Storage Stability:

After Six Months- Unworked 285 325 331. lrvorkedunl 1 358 383 4;)0+. Appearance OK OK OK.

All of the above products have properties which indicate that they are excellent traction motor gear lubricants. However, basis the ASTM penetrations and the simulated TMG torque tests which evaluates the low temperature starting properties of the lubricant, the 2% soap formulation is optimum.

A comparison of the product comprising 96 percent sulfurized residuum, 2 percent sodium tallowate and 2 percent mixed base residuum with a commercially available traction motor gear lubricant which has a large volume sale and which comprises 58 percent by volume of an unrefined residuum and 42 percent by volume of an asphaltic material obtained by air blowing of a residuum is shown in Table II.

were prepared Table II Lubricant As haltic of Exase ample 2 Lubricant ABTM Penetration, 77 F.:

Unworked 324 320. Worked 377 Too stifi. AfilloTolgBomb Oxidation Test: 33, 34 20.

r. laodi iiilr. Timken Test: 30# Load-Minutes 15,17 18.

o a Simulated 'IMG Torque Test:

Temp, F 50 50. Starting Load, Max. Watts. 3, 700 4,000+ Time on Starting Windings, Se 6 7. Mod. U. S. Steel Gear Lube Thickening Test:

Airblown, 312 Hr. at 203 F.Penetration Decrease, Percent, 77 F.:

Unworked 1 19. 3 67. Worked 2. 6 Too stlfi. Storage Stability:

AS'IM Penetration, 77 F.--

After 6 Mo.:

Unworked 325 Worked 383 Appearance OK 1 Minus sign denotes softening.

The data in Table H indicate that the product of this invention is about equivalent to the prior art product in anti-wear properties as measured by the modified four gram Timken test. However, the low temperature properties of the product, as measured by the simulated TMG torque test, are substantially better than those of the asphaltic base prior art lubricant. The superiority of the product of this invention to the prior art product is demonstrated in the Modified U. S. Steel Corporation gear lube thickening test, which is considered to be the most applicable for determining thickening resistance since it compares more directly with the dynamic oxidation conditions encountered in a churning gear case during use. In this test, the worked penetration of the prior art product could not be determined and the unworked penetration decreased 67% whilethe product of the invention showed a 19.4% increase in unworked penetration and a 2.6% increase in worked penetration.

The'traction motor gear lubricant of Example 2 (96 percent sulfur-containing residuum, 2 percent sodium tallowate and 2 percent mixed paraffin-naphthene base residuum) has been in service in two diesel locomotives for periods up to 9 months. The tests were made in switch type locomotives. The extensive nature of this service trial of the lubricant is shown in Table HI.

Periodic inspection of these locomotives indicated that excellent lubrication of the gear teeth and pinion teeth was obtained. There was no observable wear on any of the gears.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A gear lubricant comprising 1 to 3 weight percent alkali metal soap and more than 94 percent by weight of a sulfurized high viscosity petroleum residuum having a sulfur content between 0.7 and 1.3 weight percent, said residuum prior to sulfurization having an SUS viscosity at 210 F. above 950.

2. A gear lubricant according to claim 1 in which said sulfurized residuum has an SUS viscosity at 210 F. of 1000 to 1500 and is obtained by sulfurizing a residuum having an SUS viscosity at 210 F. above 950 at a temperature between 400 and 470 F. with 1.5 to 4 weight percent sulfur.

3. A gear lubricant according to claim 1 comprising 1 to 3 percent sodium tallowate and 1 to 3 percent unrefined mixed parafiin-naphthene base residuum.

4. A gear lubricant according to claim 1 comprising 95 to 97 percent sulfurized residuum, 1 to 3 weight percent alkali metal soap and 1 to 3 weight percent residuum.

5. A gear lubricant comprising 2 percent sodium tallowate, 2 percent unrefined mixed parafiin-naphthene base residuum and 96 percent of a sulfurized residuum having a sulfur content of about 0.9 weight percent and an SUS viscosity at 210 F. of about 1060, said sulfurized residuum having been obtained by sulfurizing a mixed paraflin-naphthene base residuum having an SUS viscosity at 210 F. of 1110 with 2 weight percent sulfur at a temperature about 440 F.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A GEAR LUBRICANT COMPRISING 1 TO 3 WEIGHT PERCENT ALKALI METAL SOAP AND MORE THAN 94 PERCENT BY WEIGHT OF A SULFURIZED HIGH VISCOSITY PETROLEUM RESIDUUM HAVING A SULFUR CONTENT BETWEEN 0.7 AND 1.3 WEIGHT PERCENT, SAID RESIDUUM PRIOR TO SULFURIZATION HAVING AN SUS VISCOSITY AT 210*F. ABOVE
 950. 